Is your new footer replacing the existing footer that is always displayed? If so, if you've replaced the existing footer then if you've created it with Aikau then you should just be able to add a button as normal - I'm guessing that you've not done this though from your description.
There are actually two versions of the footer - the original YUI2 based one that is shown on most pages, and the pure Aikau version that is shown on the all-Aikau pages (such as search, search manager, etc).
To add an Aikau button then you should just create an extension to insert the button into the model... if you're not able to do this then you're almost certainly not customizing an Aikau page or Aikau rendered content - in this case you probably shouldn't be trying to use an Aikau widget at all, but instead should be using a YUI2 button.
